SOUNDVIEW — Before cracking open that start-of-the-year book staple, “First Day Jitters,” second-grade teacher Elizabeth Brodbar asked her students Monday morning how they felt.

Hot, tired, hungry, shy and nervous, but happy, replied several students at Icahn Charter School 7, one of four new charters opening in The Bronx this year.

“You know what, boys and girls?” Brodbar said in a soothing voice, while Schools Chancellor Dennis Walcott and a scrum of reporters looked on. “A lot of the feelings you shared with me are what it’s like to have the jitters.”

As the new school year began Monday, on the eve of the city’s primary elections, it’s likely that students aren’t the only ones at charter schools with jitters.

After three terms of the fiercely pro-charter Mayor Michael Bloomberg, the city’s charter schools now face several Democratic mayoral candidates who are openly leery of such schools, including front-runner Bill de Blasio, who has proposed charging charters in public buildings rent and slowing their growth.

Bloomberg’s decision to allow charters to share space, or “co-locate,” with district schools free of charge is widely credited with enabling the number of charters to balloon from 17 when he took office in 2002 to 183 this year. (There are 48 charters in The Bronx, second only to Brooklyn.)

Walcott on Monday echoed the administration’s concern that the next mayor could reverse its pro-charter policies, which he said would deny parents the options they deserve.

“For any candidate to talk about choking off that type of choice is truly unfortunate,” he said in the Story Avenue building now shared by Icahn 7 and P.S. 93.

The future of the charter-school movement will have an outsize impact in The Bronx, which has some of the city’s lowest-performing district schools and — some say as a result — the greatest number of charter-school applicants.

More than 24,600 families entered lotteries for The Bronx’s 4,116 charter-school seats this year — more applicants than in any other borough, even though Brooklyn and Manhattan both had more open seats, according to estimates from the New York City Charter School Center.

Meanwhile, Bronx public-school students had some of the city’s lowest pass rates on this year’s state exams. For example, only 16 percent of Bronx fourth graders passed the English tests, while 27 percent passed citywide and 34 percent did in Manhattan.

Walcott said Monday he was “not sure there’s a direct correlation” between the Bronx’s low test scores and high number of charter-school applications. He also noted recent DOE initiatives, from expanded pre-K and after-school slots to more teacher training, to support district schools.

“I believe in our charters, but I also truly believe in our district schools,” he said.

The top two Republicans running for mayor, John Catsimatidis and Joe Lhota, both staunchly support the growth of charter schools, which are privately run but publicly funded.

The Democratic mayoral candidates, however, hold mixed views on charters.

City Council Speaker Christine Quinn and Bill Thompson, who the city teacher’s union has endorsed, both back charters and co-location, though they have promised to reconsider how space is allotted.

But Comptroller John Liu and de Blasio, the public advocate, have come out against the rapid expansion of charters under Bloomberg, which they say has detracted from district schools.

De Blasio, who has topped recent polls, has said the city does not need any new charters, that the co-location process should be suspended and that existing charters in public-school buildings should pay rent.

Walcott panned that proposal Monday.

“To charge charters rent, I think, would be totally unfortunate and would destroy the charter movement we’ve started here in New York City,” he said.

The prospect of a charter-skeptical mayor has shaken the city’s charter community, said David Golovner, the Charter School Center’s vice president of policy and advocacy.

“Given that we’ve been living for 12 years with a mayor who has really tried to help the sector grow, losing that [amidst] uncertainty of who will come in next, everybody is uneasy and anxious,” Golovner said.

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